Wafer stage and method of manufacturing the same

ABSTRACT

A wafer stage includes an electrostatic chuck (ESC) plate, an upper supporting plate, a lower supporting plate and a temperature controller. The ESC plate includes a first surface that supports a wafer. The upper supporting plate is bonded to a second surface of the ESC plate opposite to the first surface. The lower supporting plate overlaps the upper supporting plate. The temperature controller is disposed between the upper supporting plate and the lower supporting plate. The ESC plate includes ceramics. The upper supporting plate includes a composite material of aluminum or aluminum alloy and ceramics or carbon. The ESC plate and the upper supporting plate are directly bonded to each other by a room temperature solid bonding process. Thus, the wafer stage has sufficient strength to withstand pressure differences between a vacuum and atmospheric pressure, improved temperature response by minimizing heat capacity, and prevents warpage of the ESC plate.

CROSS-RELATED APPLICATION

This application claims priority under 35 USC § 119 from, and thebenefit of, Japanese Patent Application No. 2018-212815, filed on Nov.13, 2018 in the Korean Intellectual Property Office (KIPO), and KoreanPatent Application No. 10-2018-0170782, filed on Dec. 27, 2018 in theKorean Intellectual Property Office (KIPO), the contents of both ofwhich are herein incorporated by reference in their entireties.

BACKGROUND 1. Technical Field

Exemplary embodiments are directed to a wafer stage and a method ofmanufacturing the same. More particularly, exemplary embodiments aredirected to a wafer stage that can receive a wafer, and a method ofmanufacturing the wafer stage.

2. Discussion of the Related Art

In processes for manufacturing a semiconductor device using anapparatus, temperature dependency of any one of the processes, forexample, an etching process, can increase due to a fine pitch of apattern, an aspect ratio, etc., of the semiconductor. Thus, a margin oftemperature control in the processes decreases. In particular, thetemperature may need to be carefully controlled in the processes.

SUMMARY

Exemplary embodiments provide a wafer stage that has sufficient strengthto withstand the pressure difference between a vacuum and atmosphericpressure, improved temperature control by minimizing the heat capacity,and prevents warpage of the electrostatic chuck plate.

Exemplary embodiments also provide a method of manufacturing theabove-mentioned wafer stage.

According to exemplary embodiments, there is provided a wafer stage. Thewafer stage may include an electrostatic chuck (ESC) plate, an uppersupporting plate, a lower supporting plate and a temperature controller.The ESC plate includes a first surface that supports a wafer. The uppersupporting plate is bonded to a second surface of the ESC plate oppositeto the first surface. The lower supporting plate overlaps the uppersupporting plate. The temperature controller is disposed between theupper supporting plate and the lower supporting plate. The ESC plateincludes ceramics. The upper supporting plate includes a compositematerial of aluminum or aluminum alloy and ceramics or carbon. The ESCplate and the upper supporting plate are directly bonded to each otherby a room temperature solid bonding process.

According to exemplary embodiments, there is provided a method ofmanufacturing a wafer stage. The wafer stage includes an electrostaticchuck (ESC) plate, an upper supporting plate, a lower supporting plateand a temperature controller. The ESC plate includes a first surfacethat supports a wafer. The upper supporting plate is bonded to a secondsurface of the ESC plate opposite to the first surface. The lowersupporting plate overlaps the upper supporting plate. The temperaturecontroller is disposed between the upper supporting plate and the lowersupporting plate. The ESC plate includes ceramics. The upper supportingplate includes a composite material of aluminum or aluminum alloy andceramics or carbon. The method of manufacturing the wafer stage includesforming a middle layer between the ESC plate and the upper supportingplate, and directly bonding the ESC plate to the upper supporting plateusing a room temperature solid bonding process.

According to exemplary embodiments, there is provided a wafer stage thatincludes an electrostatic chuck (ESC) plate, an upper supporting plate,a lower supporting plate, a Peltier element, and a flexible thermalconductive sheet. The electrostatic chuck (ESC) plate includes a firstsurface on which a wafer is placed. The upper supporting plate is bondedto a second surface of the ESC plate opposite to the first surface. Thelower supporting plate overlaps the upper supporting plate. The Peltierelement is disposed between the upper supporting plate and the lowersupporting plate. The flexible thermal conductive sheet is disposedbetween the Peltier element and the upper supporting plate. The ESCplate and the upper supporting plate are directly bonded to each otherby a room temperature solid bonding process.

According to exemplary embodiments, the wafer stage may have thesufficient strength for withstanding the pressure difference between thevacuum and the atmospheric pressure, the improved temperatureresponsibility by minimizing the heat capacity, and the warpageprevention of the ESC plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a wafer stage in accordance withexemplary embodiments.

FIG. 2 is an exploded perspective view of a wafer stage in FIG. 1.

FIG. 3 is a graph showing increasing/decreasing temperature change ratesin the wafer stage with respect to heat capacity of an upper supportingplate and an ESC plate.

FIG. 4 is a graph showing thermistor temperatures with respect to time.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, exemplary embodiments will be explained in detail withreference to the accompanying drawings.

FIG. 1 is a cross-sectional view of a wafer stage in accordance withexemplary embodiments, and FIG. 2 is an exploded perspective view of awafer stage in FIG. 1.

Referring to FIGS. 1 and 2, according to an embodiment, a wafer stage 10includes an ESC plate 11, an upper supporting plate 12, a Peltierelement 13 and a lower supporting plate 14. The lower supporting plate14, the Peltier element 13, the upper supporting plate 12 and the ESCplate 11 are sequentially stacked. The Peltier element 13 functions as atemperature controller. A thermal conductive sheet 15 is disposedbetween the Peltier element 13 and the upper supporting plate 12.

According to an embodiment, when the wafer stage 10 is used, a wafer W,such as a silicon wafer, is placed on a first surface 11 a of the ESCplate 11. In exemplary embodiments, the first surface 11 a of the ESCplate 11 corresponds to an upper surface of the ESC plate 11. The ESCplate 11 includes ceramics. For example, the ESC plate 11 includes atleast one of SiC, alumina (Al₂O₃) or AlN.

In exemplary embodiments, the ESC plate 11 includes a composite materialof alumina and SiC. The ESC plate 11 may be a Johnson Rahbeck (JR) forcetype, a Coulomb force type, etc. An internal electrode that generates anelectrostatic force is formed in the ESC plate 11. A voltage of about±100V˜about 500V is applied to the internal electrode of a JR force typeESC plate. A voltage of about ±1,000V˜about 8,000V is applied to theinternal electrode of a Coulomb force type ESC plate.

According to an embodiment, a thermal conductive gas passageway 21 isformed in the ESC plate 11. A thermal conductive gas such as helium,which has a high thermal conductivity [0.1442 W/mk (0° C.)], is suppliedto the first surface 11 a of the ESC plate 11 through the thermalconductive gas passageway 21 so that heat from the Peltier element 13 iseffectively transferred between the wafer W and the first surface 11 aof the ESC plate 11.

According to an embodiment, when the wafer stage 10 is installed in asemiconductor fabrication apparatus, the upper supporting plate 12 isdisposed at a boundary between a vacuum environment in a vacuum chamberof the semiconductor fabrication apparatus and an atmosphericenvironment of other regions of the semiconductor fabrication apparatus.The upper supporting plate 12 has a first surface 12 a that correspondsto the vacuum environment and a second surface 12 b that corresponds tothe atmospheric environment. The first surface 12 a corresponds to anupper surface of the upper supporting plate 12. The second surface 12 bcorresponds to a lower surface of the upper supporting plate 12. Thus,the upper supporting plate 12 has a material and thickness that ispressure resistant with respect to a pressure difference of about atleast 1 atmospheric pressure.

According to an embodiment, the upper supporting plate 12 includes acomposite material of aluminum or aluminum alloy and ceramics or carbon.For example, the ceramics include at least one of SiC, alumina (Al₂O₃)or AlN.

According to an embodiment, the upper supporting plate 12 has acomposition ratio that has a thermal expansion coefficient of no greaterthan about ±5% with respect to the ESC plate 11. In exemplaryembodiments, the upper supporting plate 12 includes a metal matrixcomposite (MMC) of about 29% Al and about 71% SiC. The MMC has anelectric resistance substantially the same as that of Al. The MMC has athermal expansion coefficient substantially similar to that of thematerial of the ESC 11, such as the composite material of alumina andSiC. Therefore, warpage or delamination caused by a thermal expansiondifference is prevented between the upper supporting plate 12 and theESC plate 11 bonded to each other.

According to an embodiment, the MMC in the upper supporting plate 12 isformed by a pressure infiltration process in which Al infiltrates into aSiC madreporite by a pressure or a vacuum infiltration process in whichAl infiltrates into the SiC madreporite under vacuum. The MMC in theupper supporting plate 12 has a porosity of no more than about 1%.Further, gasses are not expelled from pores of the MMC by heating.

According to an embodiment, the first surface 12 a of the uppersupporting plate 12 is directly bonded to a second surface 11 b of theESC plate 11 opposite to the first surface 11 a by a room temperaturesolid bonding process. When the upper supporting plate 12 and the ESCplate 11 are bonded to each other by a room temperature solid bondingprocess, a middle layer is disposed between the upper supporting plate12 and the ESC plate 11. The upper supporting plate 12 and the ESC plate11 are pressurized to each other to diffuse components into the middlelayer, thereby directly bonding the upper supporting plate 12 and theESC plate 11 to each other.

According to an embodiment, the middle layer used in the roomtemperature solid bonding process includes a metal that may have lowself-activation energy and a high diffusion coefficient or an amorphousceramics having good surface flatness. For example, the middle layerincreases surface smoothness between the second surface 11 b of the ESCplate 11, which has low surface smoothness due to the large grains ofSiC, and the first surface 12 a of the upper supporting plate 12 topromote the room temperature solid bonding process.

According to an embodiment, the middle layer used in the roomtemperature solid bonding process includes a metal layer that includesat least one of Al, Ti, Ni, Au, Ag, Cu, In or Sn, or an amorphousceramics such as SiO₂, SiN, etc. In exemplary embodiments, when theupper supporting plate 12 and the ESC plate 11 are bonded to each otherby a room temperature solid bonding process, an Al layer having athickness of about 10 μm is formed on the first surface 12 a of theupper supporting plate 12 to form a mirror surface. A pressure of about200 kN is applied to the upper supporting plate 12 and the ESC plate 11for about 2 hours under atmospheric pressure or a vacuum to bond theupper supporting plate 12 and the ESC plate 11 to each other.

According to an embodiment, before performing the room temperature solidbonding process, a mirror grinding is performed on the second surface 11b of the ESC plate 11. The Al layer on the first surface 12 a of theupper supporting plate 12 is removed under a reduction atmosphere.Further, the middle layer includes a gradient material formed by mixingthe material of the upper supporting plate 12 with alumina.

According to an embodiment, the middle layer includes at least twodifferent layers that overlap each other. By using a multi-layeredmiddle layer, a middle layer that has an optical material can beselected to smooth the second surface 12 b of the upper supporting plate12 and the first surface 11 a of the ESC plate 11.

According to an embodiment, the Peltier element 13 includes athermoelectric element that converts electric energy into thermalenergy. When a potential difference is generated between electrodes atboth ends of a thermoelectric element, a temperature difference isgenerated between both ends of the thermoelectric element. The Peltierelement 13 can be classified into a uni-leg type Peltier element thatincludes thermoelectric elements with a same semiconductor type, or a πtype Peltier element that includes an N type thermoelectric element anda P type thermoelectric element. In exemplary embodiments, the Peltierelement 13 includes a π type Peltier element that effectively performsthe thermoelectric conversion.

According to an embodiment, the plurality of the Peltier elements 13 aredisposed between the upper supporting plate 12 and the lower supportingplate 14. In exemplary embodiments, about 150 to about 160 Peltierelements 13 that have a diameter on which a 300 mm diameter wafer W canbe placed are provided in the wafer stage 10. For example, the Peltierelements 13 occupy an area of no less than about 45% of that of a firstsurface 14 a in the lower supporting plate 14.

According to an embodiment, each of the Peltier elements 13 may providethe first surface 11 a of the ESC plate 11 with a heat change rate in atemperature range from about 30° C. to about 80° C. of no less thanabout 1° C./s and a cooling rate of no less than about 0.6° C./s. Thetemperature of the wafer W on the ESC plate 11 can be rapidly controlledwithout a time-lag by using the Peltier elements 13.

According to an embodiment, each of the Peltier elements 13 includes athermistor. The 150-160 Peltier elements are independently controlled.When the wafer W on the ESC plate 11 has a diameter of about 300 mm,each 20 mm×20 mm region on the wafer W can be accurately heated orcooled. Further, the wafer W is provided with a uniform temperaturewithout a temperature gradient. Furthermore, a temperature of each ofthe regions on the wafer W can be independently changed.

In exemplary embodiments, the temperature controller includes thePeltier element 13 but is not restricted to specific elements. Forexample, a plurality of thin heaters can be disposed on a lowersupporting plate 14 that has a cooling passageway. The first surface 11a of the ESC plate 11 is heated by the thin heaters. In contrast, acooling agent can be supplied to the lower supporting plate 14 throughthe cooling passageway to stop the thin heaters from dissipating heat.

According to an embodiment, a thermal conductive sheet 15 is disposedbetween the Peltier element 13 and the upper supporting plate 12. Forexample, the thermal conductive sheet 15 includes a flexible sheetmaterial, such as a silicon sheet, that has a thermal conductivity of noless than about 1 w/mK. The silicon sheet is formed by adding carbon tosilicon to improve the thermal conductivity. The silicon sheet has anoptimal concentration of carbon that improves the thermal conductivityand decreases flexibility of silicon caused by the added carbon. Thethermal conductive sheet 15 has hardness of no more than Asker C20. Thethermal conductive sheet IS has a thickness of about 0.3 mm to about 1.0mm in the absence of a load.

According to an embodiment, the thermal conductive sheet 15 isvertically compressed between the Peltier element 13 and the uppersupporting plate 12 by using a screw 23 to combine the upper supportingplate 12 with the lower supporting plate 14. The thermal conductivesheet 15 decreases thermal contact resistance between the Peltierelement 13 and the upper supporting plate 12. The thermal conductivesheet 15 may absorb displacement of the upper supporting plate 12 causedby thermal deformation of the upper supporting plate 12 to stablytransfer heat between the Peltier element 13 and the wafer W.

According to an embodiment, the lower supporting plate 14 has a firstsurface 14 a that makes contact with the Peltier element 13. The firstsurface 14 a of the lower supporting plate 14 corresponds to an uppersurface of the lower supporting plate 14. The lower supporting plate 14supports the Peltier element 13 and the upper supporting plate 12. Thelower supporting plate 14 includes a material having a Young's Modulusof no less than about 120 MPa. A material that has a Young's Modulus ofno less than about 120 MPa increases the strength of the lowersupporting plate 14. Further, a material that has a Young's Modulus ofno less than about 120 MPa prevents warpage of the lower supportingplate 14 caused by a pressure difference between atmospheric pressureand the vacuum.

According to an embodiment, the lower supporting plate 14 includes amaterial that has at least one of Ti, Ti alloy, carbon, Si, SiC, Al₂O₃,BN or ZrO₂. In exemplary embodiments, the lower supporting plate 14includes an MMC that is about 29% Al and about 71% SiC. The Al is A6061.

According to an embodiment, the MMC in the lower supporting plate 14 isformed by a pressure infiltration process in which Al infiltrates into aSiC madreporite by a pressure or a vacuum infiltration process in whichAl infiltrates into the SiC madreporite under vacuum. The MMC in thelower supporting plate 14 has a porosity of no more than about 1%.Further, gasses are not expelled from pores of the MMC by heating.

According to an embodiment, a plurality of cooling passageways 22 may beformed in the lower supporting plate 14. A cooling agent flows throughthe cooling passageways 22. To form a cooling passageway 22, the lowersupporting plate 14 is vertically divided into first and second plates.A plurality of grooves may be formed at the first plate. The first platethat has the grooves is bonded to the second plate to form the lowersupporting plate 14 with the cooling passageways 22.

According to an embodiment, the cooling agent includes refrigerants suchas organic refrigerants such as Freon, water, etc. The cooling agent iscirculated through a radiator. When the Peltier elements 13 cool thewafer W, the cooling agent flows through the cooling passageway 22 inthe lower supporting plate 14 to rapidly absorb heat in the lowersupporting plate 14 and prevent the Peltier elements 13 fromoverheating. Thus, the Peltier elements 13 can effectively cool thewafer W.

According to an embodiment, the upper supporting plate 12 and the lowersupporting plate 14 are combined with each other using the screw 23. Thescrew 23 is inserted into a screw hole 24 that penetrates through thelower supporting plate 14. The screw 23 threadedly combines with athreaded portion 25 that vertically extends from the second surface 12 bof the upper supporting plate 12. Thus, the Peltier elements 13 betweenthe upper supporting plate 12 and the lower supporting plate 14 arefixed by the screw 23.

According to an embodiment, to prevent an abnormal discharge from beinggenerated between the upper supporting plate 12 and the lower supportingplate 14 caused by an RF current, atmospheric pressure is appliedbetween the upper supporting plate 12 and the lower supporting plate 14.To ensure pressure resistivity between the atmospheric environmentbetween the upper supporting plate 12 and the lower supporting plate 14,and the vacuum environment at the ESC plate 11, about 30˜40 screws 23separated by uniform intervals are disposed between the upper supportingplate 12 and the lower supporting plate 14.

According to an embodiment, a spacer 26 is placed around each screw 23.The spacer 26 uniformly maintains a gap between the upper supportingplate 12 and the lower supporting plate 14. Thus, although the screws 23may have different fixing pressures, the gap between the uppersupporting plate 12 and the lower supporting plate 14 is maintained bythe spacer 26. Further, deviations of the thermal conductivities of thePeltier elements 13 can be prevented.

According to an embodiment, a release-preventing member is provided witheach of the screws 23. The release-preventing member prevents a releaseof the screw 23 to provide a uniform fixing pressure to the uppersupporting plate 12 and the lower supporting plate 14, which can preventdeviations in the thermal conductivities of the Peltier elements 13.

According to an embodiment, a total value of a heat capacity from thesecond surface 12 b of the upper supporting plate 12 to the firstsurface 11 a of the ESC plate 11 of the wafer stage 10 is no more thanabout 3.0 J/K per unit area. By maintaining a total heat capacity valueof no more than about 3.0 J/K, the heat in the Peltier elements 13 canbe rapidly transferred to the first surface 11 a of the ESC plate 11. Asa result, the temperature of the wafer stage 10 can be accuratelycontrolled in accordance with temperature changes of the wafer W.

According to exemplary embodiments, the upper supporting plate 12includes a composite material comprised of aluminum or an aluminum alloyor ceramics or carbon to provide a wafer stage with a sufficientstrength to endure pressure difference between an atmosphericenvironment and a vacuum environment.

Further, according to an embodiment, the ESC plate 11 and the uppersupporting plate 12 are directly bonded to each other by a roomtemperature solid bonding process. Thus, the thermal conductivity andthe temperature response between the ESC plate 11 and the uppersupporting plate 12 are improved as compared to using an adhesivebetween the ESC plate 11 and the upper supporting plate 12. Further, bydirectly bonding the ESC plate 11 to the upper supporting plate 12, thebonding strength between the ESC plate 11 and the upper supporting plate12 is reinforced and warpage of the ESC plate 11 caused by thermalexpansion can be prevented. As a result, the wafer stage 10 can firmlyfix the wafer W.

According to an embodiment, a semiconductor fabrication apparatus thatprocesses a wafer W on the wafer stage 10 includes an etching apparatus,a CVD apparatus, a sputtering apparatus, etc. By incorporating the waferstage 10 into a semiconductor fabrication apparatus, a semiconductorfabrication apparatus can be implemented with the wafer stage 10 thathas sufficient strength to endure pressure differences and improvedtemperature response without warpage of the ESC plate 11 caused bythermal expansion. When using a corrosive gas in the etching apparatusor the CVD apparatus, a corrosion-resistive layer such as alumina,yttrium oxide, etc., is coated on the wafer stage 10.

According to embodiments, the increasing and decreasing rates oftemperature change in the wafer stage have been verified. The increasingand decreasing temperature change rates were dependent on the drivingcapacity of the Peltier element and the thermal conductivity and theheat capacity of the upper supporting plate and the ESC plate. Thus, asample 1 of the upper supporting plate of SUS304 having a thickness ofabout 6 mm, a sample 2 of the MMC having a thickness of about 1 mm, asample 3 of the MMC having a thickness of about 3 mm, and a sample 4 ofthe MMC having a thickness of about 6 mm were prepared. The increasingand decreasing temperature change rates with respect to the samples 1 to4 were measured. Temperature change rates on the first surface of theESC plate between 30° C. to 80° C. under a condition that thetemperature of the lower supporting plate was fixed to 50° C. weremeasured and measured results were shown in FIG. 3.

The Peltier element was a 72 series produced by Ferrotec Corporation. Amaximum value of a driving power in the Peltier element was 4.3V and 3 Aper unit. Because a cooling rate of no less than about 1° C./sec wasrequired in view of a process, the total value of the heat capacity ofthe upper supporting plate and the ESC plate per unit area was no morethan about 6.01/K. FIG. 4 shows measured increasing and decreasingtemperatures of the samples 1 and 4. As shown in FIG. 4, alumina havinga thickness of about 1 mm was formed on the MMC of an ESC plate having athickness of about 3 mm by a solid diffusion bonding process tomanufacture a wafer stage having desired characteristics.

The foregoing is illustrative of exemplary embodiments and is not to beconstrued as limiting thereof. Although a few exemplary embodiments havebeen described, those skilled in the art will readily appreciate thatmany modifications are possible in the exemplary embodiments withoutmaterially departing from novel teachings and advantages of the presentinvention. Accordingly, all such modifications are intended to beincluded within the scope of the present invention as defined in theclaims. Therefore, it is to be understood that the foregoing isillustrative of various exemplary embodiments and is not to be construedas limited to the specific exemplary embodiments disclosed, and thatmodifications to the disclosed exemplary embodiments, as well as otherexemplary embodiments, are intended to be included within the scope ofthe appended claims.

What is claimed is:
 1. A wafer stage comprising: an electrostatic chuck(ESC) plate that includes a first surface on which a wafer is placed; anupper supporting plate bonded to a second surface of the ESC plateopposite to the first surface; a lower supporting plate that overlapsthe upper supporting plate; and a temperature controller disposedbetween the upper supporting plate and the lower supporting plate,wherein the ESC plate comprises a material that includes ceramics, theupper supporting plate comprises a composite material of aluminum oraluminum alloy and ceramics or carbon, and the ESC plate and the uppersupporting plate are directly bonded to each other by a room temperaturesolid bonding process.
 2. The wafer stage of claim 1, wherein theceramics comprises at least one of SiC, Al₂O₃ or AlN.
 3. The wafer stageof claim 1, wherein the composite material of the upper supporting platehas a porosity of no more than 1%.
 4. The wafer stage of claim 1,wherein the upper supporting plate has a thermal expansion coefficientof no greater than ±5% of that of the ESC plate.
 5. The wafer stage ofclaim 1, wherein the temperature controller comprises a Peltier element.6. The wafer stage of claim 5, wherein the Peltier element comprises aplurality of elements, and each of the Peltier elements is independentlycontrolled.
 7. The wafer stage of claim 5, wherein the Peltier elementoccupies an area of no less than about 45% of an area of a first surfaceof the lower supporting plate.
 8. The wafer stage of claim 5, whereinthe Peltier element provides the first surface of the ESC plate with aheat change rate of no less than 1° C./sec in a temperature range from30° C. to 80° C. and a cooling change rate of no less than 0.6° C./sec.9. The wafer stage of claim 5, further comprising a flexible thermalconductive sheet disposed between the Peltier element and the uppersupporting plate.
 10. The wafer stage of claim 9, wherein the thermalconductive sheet has a thermal conductivity of no less than about 1w/mK.
 11. The wafer stage of claim 9, wherein the thermal conductivesheet has a thickness from 0.3 mm to 1.0 mm, absent a load to thethermal conductive sheet.
 12. The wafer stage of claim 9, wherein thethermal conductive sheet has hardness of no more than Asker C20.
 13. Thewafer stage of claim 1, wherein the lower supporting plate has a coolingpassageway through which a cooling agent flows.
 14. The wafer stage ofclaim 1, wherein the lower supporting plate includes a material that hasa Young's Modulus of no less than about 120 MPa.
 15. The wafer stage ofclaim 14, wherein the lower supporting plate comprises at least one ofTi, Ti alloy, carbon, Si, SiC, Al₂O₃, BN or ZrO₂.
 16. The wafer stage ofclaim 1, wherein a total value of a heat capacity from a second surfaceof the upper supporting plate that faces the temperature controller tothe first surface of the ESC plate is no more than 3.0 J/K per unitarea.
 17. The wafer stage of claim 1, further comprising: a screw thatcombines the upper supporting plate with the lower supporting plateusing a screw; a spacer disposed around the screw to uniformly maintaina gap between the upper supporting plate and the lower supporting plate;and a release-preventing member provided with the screw.
 18. A method ofmanufacturing a wafer stage, the wafer stage being an electrostaticchuck (ESC) plate that includes a first surface on which a wafer isplaced, an upper supporting plate bonded to a second surface of the ESCplate opposite to the first surface, a lower supporting plate thatoverlaps the upper supporting plate, and a temperature controllerdisposed between the upper supporting plate and the lower supportingplate, wherein the ESC plate comprises a material that includesceramics, and the upper supporting plate comprises a composite materialof aluminum or aluminum alloy and ceramics or carbon, the methodcomprising: forming a middle layer between the ESC plate and the uppersupporting plate; and directly bonding the ESC plate to the uppersupporting plate using the middle layer by using a room temperaturesolid bonding process.
 19. The method of claim 18, wherein the middlelayer comprises at least one of Al, Ti, Ni, Au, Ag, Cu, In, Sn, Si orSiO₂.
 20. A wafer stage comprising: an electrostatic chuck (ESC) platethat includes a first surface on which a wafer is placed; an uppersupporting plate bonded to a second surface of the ESC plate opposite tothe first surface; a lower supporting plate that overlaps the uppersupporting plate; a Peltier element disposed between the uppersupporting plate and the lower supporting plate; and a flexible thermalconductive sheet disposed between the Peltier element and the uppersupporting plate, wherein the ESC plate and the upper supporting plateare directly bonded to each other by a room temperature solid bondingprocess.